This invention relates to a joining construction and a method of joining metal members, and more particularly to a method suitable for joining a rotary shaft and a rotary member of metal by inserting the former into the latter so that metal flow takes place in a manner creating tight contact between parts thereof.
There is a widely known joint by which a shaft, knurled by rolling a knurling tool on the surface thereof, is forcedly inserted in a smooth cylindrical hole of a member of metal. This joint forms a weak connecting of the shaft to the member and the amount of torque transmissible thereby is low, because projections provided on the surface of the rotary shaft by rolling of the knurling tool each are small in the extent of the projections which cut into the member, and pressure angle of the projection is large. As compared with a conventional joint formed by a sliding fit or pressure fit of an involute splined shaft or a serrated shaft, the joint structure of the knurled shaft is able to obtain only a third as large a transmissible torque as that obtained by the splined or serrated shaft. Further, in the joint of the knurled shaft and the member with a hole, quantities of the projections cutting into an inner face of the hole into which the shaft is inserted are not uniform on the periphery of the shaft. Therefore, substantially high concentricity between the knurled shaft and the hole can not be obtained. The knurled shaft itself is bent a little when knurled, and the knurled shaft is further bent when it is inserted in the hole of the member.
A method of forcedly inserting a shaft of a titanium alloy into holes of aluminum by pressing it, to join the aluminum plates is proposed in Japanese Patent Publication No. 48-13894 (1973). In this method, the shaft is provided with a plurality of lobes each extending axially and arranged on the circumference at equal intervals. The lobes have arcuate mountain portions and arcuate valley portions which alternatively appear and form a continuous surface. The mountain portions and the valley portions each are separated radially from a basic nominal diameter by substantially equal distances. The lobes, which are made by rolling, are in uniform contact with the aluminum plates to prestress them uniformly. The aluminum plates are fastened by a nut which is screwed up by utilizing residual stress in the plates due to compression stress prestressed to the aluminum plates.
In this method, however, the joint cannot be expected to transmit a substantially high torque because the pressure angle is large and the extent of the lobes cutting into the aluminum plate is small. Further, it is difficult to provide a joint with high concentricity between the shaft and the axis of the holes of the aluminum plates, since the dimensions and shapes of the lobes greatly influence the extent to which the lobes cut into the aluminum plate. Therefore, the joint is not suitable for joining a rotary shaft and rotary members together.